The present invention relates generally to hydraulic brake systems. More particularly the present invention relates to a non-powered evacuation and fill valve assembly and a method for using the same in connection with a hydraulic brake system.
Air within a hydraulic brake system will be compressed as the pressure within the system increases. This action reduces the amount of force that can be transmitted by the fluid. Therefore, it is important to keep all air out of the hydraulic system.
In vehicles, when an anti-lock brake system(ABS) unit is installed, air is evacuated from the hydraulic circuit before the unit is pre-filled with brake fluid. During the evacuation and fill process, solenoid valves for each brake circuit must be actuated. To effectuate the activation of the solenoid valves, a number of conventional designs require the connection of an electrical supply to the unit. However, this connection results in increased cycle time and cost in the vehicle assembly line.
Other conventional designs incorporate a spring-biased, normally closed, rubber check valve in which a very low spring force is applied to allow the valve to open during evacuation. However, during normal braking operations involving a sudden pedal release, the spring force is often not sufficient to keep the valve in the closed position. This situation can permit air to enter through the accumulator seals and result in a xe2x80x9csoftxe2x80x9d pedal, which can lead to eventual brake failure.
The present invention recognizes the disadvantages and limitations commonly associated with conventional hydraulic brake systems. Moreover, the present invention essentially utilizes a pressure differential or plug expansion to provide a xe2x80x9clatchingxe2x80x9d or xe2x80x9clockingxe2x80x9d effect in connection with a non-powered evacuation and fill valve assembly. In the context of the present invention, the term xe2x80x9cnon-poweredxe2x80x9d means without the use of an external electric connection.
In one embodiment of the present invention, the evacuation and fill valve assembly is comprised of a valve and valve plate that connects low pressure and high pressure lines in each brake circuit. The assembly evacuates the air out of every part of the hydraulic cylinder unit and is typically switched on only once during the evacuation and pre-filling process (to evacuate air). Thereafter, the assembly typically remains in the closed position.
During the evacuation of air from the system, the aforementioned assembly stays open to allow air to be evacuated from the low pressure line. During fill or during subsequent testing and thereafter, the assembly remains closed to break the connection between low pressure and high pressure lines. Because the present invention makes use of a hydraulic pressure differential, there is no need for an electrical connection to actuate the solenoid valves. Further, the present invention eliminates the problem of designs that use a spring-biased rubber check valve by keeping the valve closed and secured during normal braking operations.
In another embodiment of the present invention, the evacuation and fill valve assembly is comprised of a plug that is formed of a material that expands in communication with brake fluid. After the filling process, the plug takes in and/or xe2x80x9cabsorbsxe2x80x9d brake fluid, and expands. The expanded plug establishes a permanent connection between a valve body and the valve plug. This xe2x80x9clatchedxe2x80x9d or xe2x80x9clockedxe2x80x9d condition exists as long as there is a sufficient amount of brake fluid in the system to expand the plug. As in the case of the previously mentioned, embodiment, no electrical connection is required.
In accordance with an embodiment of the present invention, a non-powered evacuation and fill valve assembly is provided that is suitable for use in connection with hydraulic brake system having a low pressure circuit, a higher pressure circuit, and a master cylinder. The assembly is comprised of a molded rubber valve including a retaining seal and a sealing area; a steel insert; and a valve plate that may include a retaining portion. During evacuation of air from the system, said rubber valve is in an open position relative to the valve plate to permit air in the low pressure circuit to flow through the evacuation and fill valve to the master cylinder. After evacuation of air from the system, a pressure differential is created on both sides of the evacuation and fill valve and it will move to a closed position relative to the valve plate and thereafter provide a tight seal as long as the system is filled with fluid.
In accordance with another embodiment of the present invention, a non-powered evacuation and fill valve assembly is provided that is comprised of a plug and a valve body. The plug is formed from a material, such as a plastic or rubber, which expands in communication with brake fluid. Preferably, the plug includes a rubber seal that, when in position, prevents air from entering the system.